Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$37.68	12.673%	$42.4552	$42.46	$42.45	$42.50
Purchase #2	$172.69	13.629%	$196.2259	$196.23	$196.25	$196.20
Purchase #3	$46.96	3.271%	$48.4961	$48.50	$48.50	$48.50
Purchase #4	$18.70	4.231%	$19.4912	$19.49	$19.50	$19.50
Purchase #5	$245.85	5.246%	$258.7473	$258.75	$258.75	$258.70
Purchase #6	$28.82	8.182%	$31.1781	$31.18	$31.20	$31.20
Purchase #7	$48.46	9.177%	$52.9072	$52.91	$52.90	$52.90
7 purchase totals =	$599.16		$649.5010	$649.52	$649.55	$649.50